Cylinder power measurements are normally based on the P-V (pressure vs. volume) diagram. Heretofore, particularly on low speed engines the P-V diagram has been plotted by a mechanical "indicator" device to provide a graphic readout. For relatively high speed engines this mechanical device is inaccurate due to the inertia of its moving parts and hence is not reliable. Instead the cylinder pressure is oftentimes measured by an electronic transducer and the "volume" parameter is derived from the crankshaft angle of rotation via a so-called "rotary function generator". Once the P-V diagram is obtained the area corresponding to the work performed is measured by means of a "planimeter" or other suitable instrument which requires manual computation. Both prior art approaches require extensive manual involvement and therein lie the disadvantages.
The disclosed measurement system of the present invention eliminates the various manual operations required of prior art systems, and further provides a continuous output corresponding to the horsepower of the selected cylinder. As will be also hereinafter apparent the present system may be part of a larger microprocessor based system which can automatically acquire and display the measurements for all cylinders of a given engine.
From the following disclosure of a preferred embodiment of the measurement system of the present invention, the system objectives hereof are as follows:
The instant measurement system is intended to measure the compression and combustion pressures and the indicated horsepower of each cylinder at periodic time intervals;
It will accommodate any piston-type engine with up to 16 cylinders driving a common crankshaft;
It will be operable to measure the crankshaft RPM;
All measurements for a particular cylinder are to be available as continuous voltage signals so that compatible analog indicators may be used; and
Measurements by the present system are possible in both the "forward" and "reverse" running engine modes.